1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device.
2. Description of the Related Art
In the field of LSI, raised source and drain regions are being developed, and the use of raised source and drain regions also in the field of thin films for manufacturing thin film transistors and the like is under consideration. In the field of LSI, a selective epitaxial method which is a high-temperature process is used to form raised source and drain regions. However, in the field of thin films, a high-temperature process cannot be used when glass substrates and the like are used, and it is difficult to achieve raised source and drain regions.
In the field of thin films, an n-type amorphous silicon (n+-Si) film is formed over a crystalline semiconductor film, and an attempt to etch the n-type amorphous silicon film without etching the crystalline semiconductor film is made by utilizing a difference in etching rate between both the films in dry etching (see Reference 1: “Raised source and drain structure of poly-Si TFT”, Shusheng He and Jershen Maa, Electrochemical Society Proceeding, Volume 98-22, pp. 204-220).
FIG. 2 shows a structure of a thin film transistor disclosed in Reference 1. In FIG. 2, a crystalline semiconductor film 1002 with a thickness of 100 nm, a gate oxide film 1003, and a gate electrode 1005 are provided over a quartz substrate or a silicon substrate 1001 provided with an oxide film with a thickness of 200 nm. N-type amorphous silicon films 1004a and 1004b with a thickness of 100 nm each are formed over the crystalline semiconductor film 1002.
Further, a silicon oxide film 1006 with a thickness of 100 nm is formed. Over and in the silicon oxide film 1006, source and drain electrodes 1007a and 1007b are formed so as to be connected to the n-type amorphous silicon films 1004a and 1004b, respectively.